Conventional storage and retrieval devices, also known as stacker cranes, can be used in automated warehouse systems which include a number of racks each having a number of transverse storage positions arranged in a spaced-apart parallel relationship. A transfer device, such as a movable carrier, is provided between or among the racks, with the space between the racks (rack aisle) serving as a travelling path.
The storage and retrieval device may comprise a cart which travels along a rail or track system placed along or adjacent to one or more of the racks. The storage and retrieval device may include a turntable arrangement and a load handling device for picking items from storage locations in the racks.
According to such conventional configurations, a combination of the rails or tracks, the movable carrier, rotation of the turntable and action of the arm/hand, serves to deliver a load between a number of transfer positions, and other identified positions within the warehouse system.
As disclosed in the conventional art, the entire operation of such a storage and retrieval device is powered electrically. Electric power is typically necessary to drive each component within the system.
However, according to the conventional storage and retrieval devices, for safety reasons, it is necessary that electrical power is able to be removed from the system when one or more doors of a switchgear cabinet, such as might be mounted on the movable carrier or cart, are opened. A monitoring device provides this function. However, conventional electrical power monitoring systems for switchgear cabinet doors require electric power. Thus, in order to continuously monitor the opened or closed states of the switchgear cabinet doors, it is necessary to have continuous electrical power to the switchgear cabinet, which, of course, defeats the purpose of the electrical power safety system, and may be contrary to safety regulations in the United States and Canada.
According to the National Fire Protection Association (NFPA79) publication, which is directed to the electrical standards for industrial machinery, an enclosure must be provided for protection in order to prevent direct contact from outside an enclosure, cf. section 6.2.2 of chapter 6. Therein. section 6.2.3 defines the requirements for enclosure interlocking, wherein “each disconnecting means mounted within or adjacent to a control enclosure that contains live parts operating at 50 volts AC (rms value) or 60 volts DC or more shall be mechanically or electrically interlocked, or both, with the control enclosure doors so that none of the doors open unless the power is disconnected. Interlocking shall be reactivated automatically when all the doors are closed.” Section 6.2.3.2 further provides that “the interlocking means shall prevent closing of the disconnecting means while the enclosure door is open, unless an interlock is operated by deliberate action.”